Tuesday, November 4, 2008

Making Biochar

It has been very encouraging to watch the expansion of interest in the subject of biochar over the past eighteen months. When I first tripped over the subject in June 2007, the primary forum on the subject went the odd day without a post. I introduced the material to Jerry Pournelle’s site at www.pournelle.com that month and the forum immediately got very active. It also helped attract the first readers to my blog for which I am grateful.

I now receive thirty to forty postings from the forum every day and I have an unbelievable 6000 such postings that I have not found the time to read in my terra preta archive to say nothing of the thousand or so that I have read. It is obvious now that folks are working with the concepts everywhere today on every continent and in every likely environment. Real farmers and real household gardeners are trying out the ideas in their own back yards.

Some very important questions have been answered. It is possible to tackle alkaline and saline soils with this protocol successfully. I thought it likely a year ago but we are getting confirmation. It is not simple but it appears that the conditioning of the soil with char allows the soil to become fertile inside of about two years. It apparently takes a growing season for the soil to be reformed after which you have what you need.

I also pointed out the utility of using seed hills in the early implementation of the biochar protocol. This allows effort to be concentrated on twenty five percent or less of the land in the early stages.

There is little apparent dispute that the working mechanism is that the carbon binds soluble nutrients in place until a root or other biological agent arrives to acquire them. This hugely lowers the need to fertilize the soils as the current massive wastage into the groundwater is hugely reduced if not almost eliminated. This is, by the way, a huge breakthrough in soil husbandry and will be rapidly accepted once it is presented this way.

The other big issue is how to make the stuff. I have introduced ideas on how the originators did it and have investigated a number of more modern systems. The interesting question is how a home gardener or an experimenter can produce a good quality biochar.

The first issue that must be tackled is the feedstock. The whole charcoal industry has predisposed thinking toward using wood. This turns out to be a bad idea. The finer the end product the better, and all wood will give is a coarse product that will be in your soil for generations. Some minor wood will not be harmful, but the majority of the feedstock needs to be non woody plant waste, well dried. Charring will reduce the weight by about eighty percent or less depending on your ability to manage air flow.

Obviously some form of commercial charcoaler will give you a better yield and perhaps a more consistent product. If you do not mind a little work, make a collar out of sheet metal in the form of a ring like a drum that can be set out in the middle of your garden or field. To allow some air flow in through the bottom, place thin branches under the edges. This will need to be experimented with. Load this ring which may be two or three feet high and perhaps four feet across, with a well packed charge of feed stock. Corn stover is certainly the most convenient and I am certain is the original feedstock in Brazil. But any available material will do, particularly for an experiment.

It then needs to be capped. A layer of soil is probably the best option, since it can be topped up whenever a breakthrough occurs. Also it is easy to leave an initial opening in the center to place the fire charge. Once the fire charge is set on top of the load, it can be capped of with a metal garbage can lid.

After all that, it is left to practice and experience to get the best result. It will take hours to completely burn through the whole load and it is likely some of the charge will not be charred at all. No harm however, as it is expedient once the fire is out the next day or so to lift off the ring and blend the biochar and capping soil and any unburnt feedstock into a homogenous product.

This should give any gardener ample material to work with particularly if he employs hills formed with a shovel full of this blend.

If you are really keen, you can review my posts from last year on the making of a corn stover earthen kiln. That is for a field of corn and a few willing backs and I believe is how the Indios made the large fields in the first place after it was first discovered as a result of backyard midden piles.

Anyway, this is as minimalist as I can make it, although an earthen wall and a stove pipe to allow air into the bottom may work well also. That can be a pit with the same stove pipe at work and that emulates some rough charcoal making where efficiency does not matter much, since they lacked the stove pipe.

I would not recommend at this time applying this method in large operations simply because the smoke and unburned gases would likely be huge. Practice may prove otherwise and assuming that a closed modern system is obviously better may well be wrong.

This should help anyone anywhere experiment with biochar, particularly where subsistence farming is practiced and the only tools available are usually strong backs.


Folke said...

I very much agree with the notion of counteracting global warming simultaneous with increasing soil fertility. However, I am uneasy about your charring method. There is a risk the fumes contain GHG:s as methane, making the sake worse and giving the method bad-will. A similarly simple method, but with a flame-off of the gasses is described on my homepage at http://www.holon.se/folke/carbon/simplechar/simplechar.shtml
Folke G√ľnther

arclein said...

Hi Folke

the problem with methane is grossly over promoted for a nomber of very good reasons, although the true belevers will never listen.

It migrates rapidly into the troposphere to start with. It really does not linger and i suspect that the science quoted is pretty suspect. what is clear is that the land halo over the ocean dimishes very quickly which simply confirms what i am saying.

more importantly, any natural production system should be designed around a charge of hot coals that burn top down creating a chimney. This chimney will draw all the production gases through the burn front eliminating all the volitiles except for CO2.

Otherwise you have a campfire and no biochar. there is some cute work here if you build an earthen kiln around these principles.

The fact is is that traditional charcoaling was based on maximising the burning of the volitiles to get the heat.